Moisture control device for centrifugal extractors



3,391,788 MOISTURE CONTROL DEVICE FOR CENTRIFUGAL EXTRACTORS Filed Aug. 11, 1966 July 9, 1968 c. F. STRANDBERG, JR.. ET

4 Sheets-Sheet l INVENTORS ATTORNEY Ge o 1V Z 3% 5y F6 I w 0% W July 9, 1968 c, STRANDBERG, JR" ET AL 3,391,788

MOISTURE CONTROL DEVICE FOR CENTRIFUGAL EXTRACTORS Filed Aug. 11, 1966 4 Sheets-Sheet 2.

METER um RLRRM 'II INVENTORS ATTORNEY y 1968 c. F. STRANDBERG, JR, ET AL 3,391,788

MOISTURE CONTROL DEVICE FOR CENTRIFUGAL EXTRACTORS 4 Sheets-Sheet 5 Filed Aug. 11, 1966 INVENTORS Char/es F S/nmaer i:

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MOISTURE CONTROL DEVICE FOR CENTRIFUGAL EXTRACTORS Filed Aug. 11, 1966 4 Sheets-Sheet 4 ATTORNEY m x 0 MW mu. w H H m I P H w u n H H a 3 E E Q s? m w m J53 mmnm 3"" A 1 2m .15 E 6 n E J y n MNK no 3 x .iT 4 i u 9 A 5 "mm 9 wit 0% mod QNM. NQA q M. 4 mm -Kmw 3mm n" E ua ur L k.

United States Patent 3,391,788 MOISTURE CONTROL DEVICE FOR CENTRIFUGAL EXTRACTORS Charles F. Strandberg, Jr., and Robert C. Strandberg,

Greensboro, N.C., assignors to Strantlberg Engineering Laboratories, Inc., Greensboro, N.C., a corporation of North Carolina Filed Aug. 11, 1966, Ser. No. 571,740 13 Claims. (Cl. 21087) ABSTRACT OF THE DISCLOSURE The apparatus includes a centrifugal extractor such as is used in laundries to spin dry wet fabrics. A perforated bowl is driven at high speed. Moisture from the fabric im pinges on a pair of electrodes which are connected to a control circuit which may either signal the operator to stop the machine or activate a stopping device to stop the machine automatically when the correct amount of extrac tion has taken place.

This invention relates to an electric moisture monitoring and control device, and more particularly to an electric conductance type moisture monitoring and control device for use in conjunction with a centrifugal extractor such as is used in laundries to remove water from the laundered fabrics.

In commercial and industrial laundries, the fabrics are first washed and rinsed, after which they are spun at very high speed either in the same machine or in a separate machine for the purpose of removing a large part of the water content. It has been determined for most cotton and linen fabrics that it is desirable to extract water until about 45% water is still contained in the fabric. Excessive extraction, in which case the fabric is too dry, prohibits the ironing or pressing operation which follows to produce a smooth surface. Instead, wrinkles and creases are not pressed fiat. Insufficient extraction, in which case the fabric is too wet, causes the fabric to turn yellow in color after ironing. It also requires excessive steam to iron dry.

An object of this invention is to provide a means for accurately determining when the correct amount of extraction has taken place and for activating a control circuit which may either signal the operator to stop the machine or activate a stopping device to stop the machine automatically.

It is another object of this invention to provide animproved moisture monitoring device of the electrical conductivity measuring type for accurately measuring a moisture condition, and operating a control relay when a predetermined moisture condition has been reached.

It is another object of this invention to provide in the moisture monitoring device of this invention a moisture detecting circuit, a moisture indicating circuit, and a high input impedance isolation amplifier connecting the moisture detecting circuit and the moisture indicating circuit. In a preferred form of this invention the isolation am- .plifier is a Darlington transistor emitter-follower which is described in greater detail subsequently in this specification.

It is another object of the invention to include calibrating means for the moisture monitor and a function switch for alternately connecting said calibrating means and said moisture measuring circuit to the aforesaid isolation amplifier.

It is another object of this invention to include in the moisture detecting device of this invention an alarm-calibrating potentiometer connected in circuit with the aforesaid isolation amplifier to develop a voltage signal which 3,391,788 Patented. July 9, 1968 "Ice varies as a function of the moisture condition detected, a triggering circuit for producing a trigger signal when the voltage signal across said potentiometer reaches a predetermined value indicative of a predetermined moisture condition, a controlled silicon rectifier gate responsive to said trigger signal, and a control relay in circuit with the controlled silicon rectifier gate to be energized when the controlled silicon rectifier gate is turned on.

It is a further object of this invention to provide an alarm indicator means which is controlled by the aforesaid control relay.

Other objects and advantages of this invention will become more apparent during the course of the following description, when taken in connection with the accompanying drawings.

In the drawings:

FIG. 1 is a front perspective view partly broken away of a centrifugal extractor incorporating the moisture monitoring detector of the invention,

FIG. 2 is a vertical sectional view through the side wall of the centrifugal extractor and moisture monitoring detector shown in FIG. 1,

FIG. 3 is a front elevational view of the moisture monitor casing including the moisture condition indicator and signal device, and

FIGS. 4a and 4b taken together form a schematic circuit diagram of the moisture monitor circuits of the invention.

Referring now to FIG. 1 of the drawings, we have shown therein a centrifugal extractor 10 such as is used in laudries to spin dry wet fabrics. The centrifugal extractor 10 consists of a perforated bowl 11 into which wet fabric is placed, a drive motor 12 and spindle 13 onto which the bowl is seated. The complete assembly is housed in a cylindrical case 14 which may be suported on a floor by feet (not shown). A drain 15 is provided in the bottom 16 of the case beneath the lower level of the perforated bowl. A cover 17 attached to the case by hinge 18 provides an access opening for the centrifugal extractor.

The wet fabric is placed around the inside of the perforated walls of the bowl 11. When power is applied to the drive motor 12, the bowl 11 is rotated so as to cause a large part of the water contained in the fabric to be forced through the perforations in the bowl wall. The water strikes the inside 19 of the outer case 14 and flows to the bottom 16 and through the drain 15. By allowing the machine to run for a certain period of time, depending upon the weight of the load of fabric, the degree of extraction can be approximately controlled.

The degree of extraction can be said to be approximately inversely proportional to the rate at which water is caused to strike the inner wall 19 of the case. During the early stage of extraction, the inner wall 19 is flooded with water. As the extraction progresses, the rate of ex traction decreases, and the propagation of water becomes somewhat like a high-velocity mist or rain, the rate of which continues to decrease with further extraction.

The amount of water striking the inner wall 19 per unit of time can be measured by placing a detector 23 having a pair of electrodes 24 and 25 in the case wall, the face of which is exposed to the high-velocity particles of water. As each quantity of water strikes the surface, it is immediately driven off by a rotating mass of air travelling in the direction of rotation of the perforated bowl. Simultaneously, new quantities of water strike the surface, and

so on as the extraction process continues. During each instant of extraction, the electrical resistance between the electrodes 24 and 25 on the exposed surface is inversely proportional to the quantity of Water on the surface, since water is a conductor of electricity. The current source in the measuring device may be either direct or alternating without incurring any effects from polarization since the water is continually moving onto and off of the surface and electrodes.

Referring to FIG. 2, the detector 23 comprises a pair of spaced electrodes 24, 25 secured to an electrically insulating disc 26 on the inside wall 19. The disc 26 is in turn secured to a threaded bushing having an enlarged disc-like portion 27 recessed to receive the insulating disc 26, and a hollow stem 28 which extends through an aperture 34 in the case wall 14. The threaded bushing 28 is held firmly in place in the case wall by a retainer nut 29. Detector leads 3%, 31 are attached at their one end to the electrodes 24 and 25 respectively, and extend through the hollow passage 33 in the bushing stem to the outside of the extractor case 14. Suitable sealing material 32 is provided to seal the hollow passage 33 around the detector leads against water leakage.

The leads 30, 31 are connected at their other end to a moisture monitoring device 35, shown in FIG. 3, and shown schematically in FIGS. 4a and 4b taken together, which is located externally of the centrifugal extractor.

Referring to FIG. 3, the moisture monitor 35 comprises a casing 36 which houses the moisture measuring circuits and switching circuits shown in FIGS. 4a and 4b. The casing may be mounted on a wall or control panel by means of screw fasteners extending through cars 37 extending outwardly from the casing side walls. In the front wall or face, of the moisture monitor casing 36 are mounted a moisture condition indicator meter M1, a function switch S1, a horn on-oif switch S4, a range potentiometer R2, a wet test switch S2, an alarm reset switch S3, a wet set potentiometer R14, an alarm calibrate potentiometer R9, and a meter calibrate potentiometer. The purpose of the aforementioned switches and controls will subsequently be described in reference to FIGS. 4a and 4b.

The moisture monitor 35 consists essentially of an improved resistance measuring device, sometimes referred to as a conductivity measuring device. To be of practical usefulness to the operator, the resistance or conductivity indicating meter M1 is calibrated in terms of DRY NORMAL, and WET, although other forms of calibration may be used without departing from the spirit of the invention. To be of additional usefulness, the device is equipped with a unique switching means connected to a horn H1 and light DS1 to signal the operator when the pointer 39 reaches NORMAL indication. A power relay (not shown) may be also incorporated in the device to de-energize the motor and, by conventional means, to actuate a brake to automatically stop the extractor when the pointer 39 reaches NORMAL indication.

After a load of fabric is placed around the inside wall of the perforated bowl 11, the operator starts the machine. At this time no water is striking the detector, so the pointer 39 rests at the extreme DRY end of the indicator scale. This condition persists until the rotational velocity of the bowl 11 is high enough for the centrifugal force produced to cause the fabric to press against the inner wall of the perforated bowl and for water to begin to pass through the perforations. When this occurs, the pointer 39 moves promptly to extreme WET end of the indicator scale as a result of the initial flooding of the detector 23 with water. Depending upon the resistance sensitivity or range of the measuring instrument, which is adjustable to permit setting the correct value for proper extraction at the NORMAL point on the indicator scale, the pointer 39 remains at the extreme WET end of the scale until the flooding condition decreases to a highvelocity, concentrated mist This may, for instance, require 30 seconds, after which the pointer 39 begins a gradual and constant movement toward the NORMAL point. This may require another 60 seconds. When the pointer 39 reaches the NORMAL point, and indicator light D51 and horn H1 are operated to signal the operator to stop the machine. Simultaneously, voltage may be removed from a power relay (not shown), the contacts of which may be connected to tie-energize the motor 12 and, by conventional means, engage the brake shoe 20 against the brake disc 21 to stop the machine automatically, if desired. In the present embodiment where the device is operated to indicate correct extraction and not automatically stop the machine a light and horn reset button 53 is provided to turn them ofi", after which they will operate again at completion of the next extraction.

The electrical circuits for the moisture monitor and control device of this invention will now be described in reference to FIGS. 4a and 4b taken together. The complete circuit diagram of the system has been divided for convenience into two figures, FIGS. 4a and 4b, where broken lines in FIG. 4a are connected to similarly designated broken lines in FIG. 4b.

Referring to FIG. 4a, AC line voltage is applied to terminals 1 and 2. Voltage is subsequently applied to the primary of transformer T1, with protective fuse F1 and one section of switch S1 in series with one side of the incoming line. The secondary of transformer T1 provides AC voltage of approximately 25 volts. This voltage is full wave rectified =by diodes X2, X3, X4 and X5 and is filtered by capacitor C2. The voltage across C2 is approximately 35 volts. This voltage is applied across series connected resistor R13 and zener diode X6. The voltage across X6, which remains constant at 12 volts over widely varying line voltages and circuit loads, provides the regulated power supply for the remainder of the circuit.

In FIG. 4b, transistors Q1 and Q2 and potentiometer R9 are connected across the power supply and form a compound emitter-follower connection commonly referred to as a Darlington emitter-follower. This type of circuit exhibits very high input resistance which is necessary to prevent loading of the input. Furthermore the emitter-follower has less than unity voltage gain (approximately .9), with the output appearing across R9. Therefore, it can be seen that the Darlington emitter-follower serves as a buffer or isolation stage to effectively isolate the high resistance of the measuring circuit from the low resistances of the indicating and controlling circuits.

The measuring circuit consists of the series connected resistor R1, potentiometer R2, and the input connector I 1, the latter being connected to the moisture detector 23 thereby displaying terminal resistance inversely pro portional to the moisture present. The junction of R1 and I1 is connected via pole 4 of function switch S1 in the ON position and through current limiting resistor R6 to the base of transistor Q1, the input of the emitterfollower. Therefore, as the voltage from the junction of resistor R1 and J1 to ground varies, as the moisture varies, the voltage across resistor R9 similarly varies. Moreover, if the moisture content increases resulting in a respective decrease in the detector resistance, then the voltage at the base of transistor Q1 with respect to ground increases, thereby increasing the voltage drop across R9.

The indicating circuit consists of resistor R10, capacitor C1, panel meter M1, resistor R12, and potentiometer R14. R10, R12, and R14 comprises a divider for dropping the voltage to the meter M1. Capacitor C1 provides damping for the meter M1.

The controlling circuit consists of the remaining parts comprised primarily of transistors Q3, Q4 and Q5, silicon controlled rectifier X7, relay K1, and horn H1. Transistors Q3 and Q4 form a standard Schmitt Trigger; transistor Q5 serves as an inverter and the silicon controlled rectifier X7 is used as a relay latching driver.

Input voltage for the control of the Schmitt Trigger circuit is taken from the variable arm on potentiometer R9, which is designated as the alarm-calibrate potentiometer, and is applied through current limiting resistor R11 to the base of transistor Q3. The Schmitt Trigger circuit including NPN transistors Q3 and Q4 is typified by a common emitter resistor R19 connecting the emitters of both Q3 and Q4 to ground. Load resistors R15 and R18 connect the collectors of Q3 and Q4 respectively to the positive 12 volt source. The voltage signal appearing at the collector of Q3 is coupled to the base of Q4 via coupling resistor R16. Base bias resistor R17 connects the base of Q4 to ground. The output signal from the Schmitt Trigger is coupled from the collector of transistor Q4 through resistor R20 to the base of transistor inverter amplifier Q5.

Transistor Q5 is a PNP transistor having its emitter connected to the positive 12 volt source and its collector connected through load resistor R22 to ground. The out put voltage signal from the inverter amplifier Q5 is coupled from the collector of Q5 to the gate of silicon controlled rectifier X7 via parallel capacitor C4 and resistor R23. Resistor R24 and capacitor C5 are connected from the gate of X7 to ground.

The silicon controlled rectifier X7 serves as a switch connected in series circuit with pole 2 of the function switch S1 (in the ON position), resistor R5, the energizing coil of relay K1, and reset switch S3 between ground and the positive voltage side of the rectified power supply. Silicon controlled rectifier X7 also serves as a switch in series circuit with resistor R8, indicator lamp DS1 and reset switch S3 between ground and the positive voltage side of the rectified power supply. The silicon controlled rectifier X7 is normally gated olf so that it acts as a high resistance block to current flow in the circuits of relay K1 and indicator lamp DS1. When a sufiicient current and voltage signal is applied to the gate of X7, the rectifier is gated on and offers a low resistance path to the current flow in the circuit of relay K1 and indicator lamp DS1. The reset switch S3 is provided so that an operator can turn off the silicon controlled rectifier and de-energize the circuits of relay K1 and indicator lamp DS1 and thus recycle the centrifugal extractor after the desired liquid extraction for a given load has been performed.

The control relay K1 may control one or more circuits to perform various functions, such as sounding an alarm,

automatically stopping the centrifugal extractor motor 12, braking the extractor etc. Contacts 1 and 2 of the relay switch are series connected in an alarm circuit with a horn H1, a manual alarm oil-on switch S4, and resistor R21 between ground and the positive side of the rectified power supply. Contacts 1 and 2 are normally open but are closed when the relay coil of K1 is energized. Contacts 3 and 4, and 5 and 6 are shown on the relay switch of K1 to indicate that other control circuits (not shown) may be provided to perform various functions. The horn H1 may be a solid-state horn or other audible alarm.

The function switch S1 is a four pole, three position manually operated switch. The three positions designated a, b and correspond to an OFF position, a calibrate position and an ON position respectively. In the OFF position all the poles are open circuited. In the calibrate position, pole .1 in the main AC power supply circuit is closed and pole 3 in the input circuit from the calibrate voltage divider network including R3 and R4 to the base of transistor Q1 is closed, poles 2 and 4 remain open. In the ON position poles 1, 2 and 4 are closed while pole 3 is open.

Operation With line voltage applied to terminals 1 and 2, with switch S1 position to off, and with moisture detector 23 essentially dry, the entire circuit is inactive. Assume that switch S1 is now positioned to Cal., the following events occur:

(1) The collector to emitter resistance of Q2 drops to approximately 10,000 ohms due to the input voltage to Q1 from the divider formed by resistors R3 and R4. This in turn yields a mid-scale reading on meter M1.

(2) Capacitor C3 delays the appearance of input voltage to the base of Q3, holding Q3 off. With Q3 olf, Q4 turns on immediately, turning Q5 on thereby pulsing the gate of X7 via C4 and R23.

(3) Silicon controlled rectifier X7 turns on due to the pulse from Q5. This provides voltage to indicator lamp DS1 through the normally closed reset switch S3.

Before calibrating the controlling circuit, the indicating meter M1 should now be calibrated. This is accomplished by depressing the WET TEST push-button switch S2 and adjusting the WET SET potentiometer R14 for full-scale indication. This action is similar to the zero adjustment on conventional ohm-meters. However, readjustment of WET SET is not required for different settings of the RANGE potentiometer R2.

Calibration of the indicating circuit is now complete. Returning to the original conditions when the circuit was first placed in operation with S1 positioned to Cal., the silicon controlled rectifier X7 is on resulting in lamp DS1 also being on.

If the Reset Switch is now depressed momentarily, X7 will turn off, and remove voltage from lamp DS1. The ALARM CAL. potentiometer R9 can now be adjusted to cause transistor Q3 to turn off. When the circuit was first placed into operation Q3 may have remained off, depending on the position of the wiper arm potentiometer R9. If R9 is turned full clockwise, this will cause Q3 to turn on. Adjustment of R9 now, slowly counterclockwise, will cause Q3 to turn off precisely at the mid-scale position of the meter. The action of Q3 turning oif results in Q4, Q5, and hence X7, all turning on.

Calibration of the controlling circuit is now complete. If function switch S1 is now positioned to ON and the Reset S3 is momentarily depressed to open X7, the entire circuit is now ready for operation. Since at the beginning of operation the moisture detector electrodes are essentially dry, as pointed out above, the resulting resistance across I1 is very high, in excess of several hundred megohms. Therefore, transistors Q1 and Q2 are ofi? and the indicating meter M1 reads at the .lowest calibrated point on the scale. With Q1 and Q2 off, and hence no voltage drop across R9, Q3 is off, and Q4 and Q5 are on. Silicon controlled rectifier X7 remains off due to the high resistance value of R23 which prevents DC operation of X7. When the extractor is turned on, the detector 23 becomes wet and its resistance drops. This causes transistors Q1 and Q2 to begin conducting with a resultant proportional meter reading. As the meter reading passes mid-scale, Q3 turns on causing Q4 and Q5 to turn otf. The meter reading progresses toward full-scale where it remains for the majority of the extraction time. As the volume of water on the detector decreases, as extraction continues, the detector resistance begin-s to increase, thereby causing a slow decrease in the meter reading. When the meter again reaches mid-scale on this downward movement, determined by the setting of the RANGE potentiometer R2, Q3 turns off. This in turn causes Q4 and Q5 to turn on. The voltage drop suddenly appearing across R22 produces a pulse via capacitor C4 and resistor R23 which turns on the silicon controlled rectifier X7. Lamp DS1 turns on; relay K1 is energized, and assuming that the alarm off-on switch S4 is on, the horn H1 produces an audible alarm. Momentarily depressing the Reset push-button S3 will reset the control circuit and the unit is ready for the next cycle.

The letters CW in FIG. 4b besides potentiome-ters R2, R9 and R14 indicate the direction of clockwise adjustrnent of the adjustable potentiometer taps.

While in the foregoing there has been described and shown the preferred embodiment of this invention, various modifications may become apparent to those skilled in the art to which the invention relates. Accordingly, it is not desired to limit the invention to this disclosure and various modifications and equivalents may be resorted to, falling within the spirit and scope of the invention as claimed.

We claim:

1. Centrifuging apparatus comprising a rotatable container for retaining wet articles, drive means for rotating said container at speeds sufiicien-t for centrifugally extracting liquid from said articles and for discharging the extracted liquid from the container, a source of electric current, a variable conductance type liquid detector means positioned radially outwardly of said container directly in the discharge path of the centrifugally extracted liquid and responsive to the extracted liquid impinging there-on for producing an electric signal which varies as a function of the rate of liquid being extracted from said articles, said liquid detector means including a pair of spaced electrodes connected in circuit with said electric current source, said spaced electrodes being mounted on an insulating surface and positioned in the path of extracted liquid so that the impinging liquid when of sufficient quantity will form a moving film bridging said electrode, said film varying in amount and in degree of electrical conductivity in proportion to the rate of liquid impingement on said detector means, and a moisture condition indicator means responsive to said electric signal for producing an indication of the moisture condition of articles in said container.

2. The apparatus set forth in claim 1 wherein said centrifuging apparatus further includes an outer tub surrounding said rotatable container, and said liquid detector means is mounted on the inside surface of said outer t-ub.

3. The apparatus set forth in claim 1 together with a control relay, and switching means in circuit with said control relay which is responsive to said electric signal for operating said relay when the rate of extraction of liquid from said articles reaches a predetermined minimum level.

4. The apparatus set forth in claim 1 wherein said spaced electrodes are thin flat plates having front and back sides, said plates being affixed to said insulating surface with their back sides adjacent to said surface and their front sides facing said container in the path of said extracted liquid, said insulating surface being uninterrupted in the area between said electrodes.

5. Centrifuging apparatus comprising a rotatable container for retaining wet articles, drive means for rotating said container at speeds sufiicient for centrifugally extracting liquid from said articles and for discharging the extracted liquid from the container, a source of electric current, a variable conductance type liquid detector means positioned radially outwardly of said container directly in the discharge path of the centrifugally extracted liquid and responsive to variations in the rate of liquid impinged thereon for producing an electric signal which varies as a function of the rate of liquid impinged thereon, said liquid detector means including a pair of spaced electrodes connected in circuit with said electric current source, said spaced electrodes being mounted on an insulating surface and positioned in the path of extracted liquid so that the impinging liquid when of sufiicient quantity will form a moving film bridging said electrode, said film varying in amount and in degree of electrical conductivity in proportion to the rate of liquid impingement on said detector means, and a moisture condition indicator means responsive to said electric signal, together with a control relay, and switching means in circuit with said control relay which is responsive to said electric signal for operating said relay when the rate of extraction of liquid from said articles reaches a predetermined minimum level, said switching means including a silicon controlled rectifier having an anode, a cathode and a gate, said silicon controlled rectifier being connected in series with a direct current source and said control relay forming a control relay circuit, and positioned so that the anode is connected to the positive side of said control relay circuit and the cathode connected to the negative side of said latter circuit, trigger means responsive to a predetermined voltage signal for opening the gate of said silicon controlled rectifier so that the silicon controlled rectifier oifers a low resistance path to current flow from anode to cathode, and adjustable means in circuit with said trigger means for selecting a predetermined voltage derived from said electric signal which will actuate said trigger to open said gate.

6. The apparatus set forth in claim 5 wherein said trigger means includes a bistable transistor multivibrator and a transistor inverter connected in cascade between said adjustable means and said silicon controlled rectifier gate.

7. The apparatus set forth in claim 5 wherein said adjustable means includes an isolation amplifier having a high impedance input terminal, and an output circuit, and a potentiometer connected in the output circuit of said isolation amplifier, said potentiometer having an adjustable ta-p connected to said trigger means a voltage divider including said pair of spaced electrodes connected in series with said current source and circuit means connecting said input terminal to said voltage divider.

8. The apparatus set forth in claim 7 wherein said isolation amplifier is a compound transistor emitter follower connected across said current source.

9. The apparatus set forth in claim 8 wherein said compound transistor emitter follower includes a pair of like transistors each having a base, a collector and an emitter, said input terminal being connected to the base of one transistor of said pair, means directly connecting the collectors of said pair of transistors together and to one side of said current source, means connecting the emitter of said one transistor to the base of the other transistor, and means connecting the emitter of said other transistor of said pair to the other side of said current source through said potentiometer.

10. The apparatus set forth in claim 5 together with a manual reset switch in said control relay circuit.

11. The apparatus set forth in claim 10 together with an alarm means which is under the control of said control relay.

12. Centrifuging apparatus comprising a rotatable container for retaining wet articles, drive means for rotating said container at speeds sufficient for centrifugally extracting liquid from said articles and for discharging the extracted liquid from the container, a source of electric current, a variable conductance type liquid detector means positioned radially outwardly of said container directly in the discharge path of the centrifugally extracted liquid and responsive to the extracted liquid impinging thereon for producing an electric signal which varies as a function of the rate of liquid being extracted from said articles, said liquid detector means including a pair of spaced electrodes connected in circuit with said electric current source, said spaced electrodes being mounted on an insulating surface and positioned in the path of extracted liquid, and means responsive to said electric signal when the rate of extraction of liquid from said articles reaches a predetermined minimum level for terminating the centrifuging operation.

13. The apparatus set forth in claim 12 together with means for selecting the minimum rate of extraction of liquid at which said means responsive to said electric signal functions to terminate the centrifuging operation.

References Cited UNITED STATES PATENTS 3,043,l25 7/1962 Horecky 6812 3,184,932 5/1965 Cobb et al. 68-12 REUBEN FRIEDMAN, Primary Examiner.

SAMIH N. ZAHARNA, Examiner.

I. ADEE, Assistant Examiner. 

